To reduce transmission time, modern voice messaging systems time compress a voice message before transmission and then time decompress, i.e., time expand, the voice message after it is received. Time compression is accomplished by removing redundancy present in the voice message. Time decompression is accomplished by adding redundancy. Removing and adding redundancy is an effective technique for compressing and decompressing voiced speech, which is teeming with redundancy.
Unfortunately, signals that have little or no redundancy, e.g., unvoiced speech and system noise, can cause undesirable artifacts in the decompressed voice message. Adding redundancy to unvoiced speech and noise can cause "warbling" sounds that are audible upon message playback.
Thus, what is needed is a method and apparatus that can minimize the undesirable artifacts produced by the time compression and decompression process when processing unvoiced speech and noise. Preferably the method and apparatus will not require a significant increase in processing power in the device receiving the voice message.